In a wireless communication system, a mobile station determines a transmission timing for a base station based on a timing advance (TA) transmitted from the base station. Accordingly, if the transmission timing of the mobile station deviates, the base station notifies the mobile station of a new TA to maintain synchronization of a radio signal from the mobile station to the base station and corrects the transmission timing of the mobile station.
Specifically, if the base station detects a deviation in the transmission timing when receiving the radio signal from the mobile station, the base station calculates the correction value of a TA, includes this correction value in a TA command (TAC), and notifies the mobile station of the TAC. Upon receiving the TAC, the mobile station corrects the TA being used based on the correction value of the TA included in the TAC, and uses the corrected TA as a new TA. This corrects the transmission timing of the mobile station.
In Long Term Evolution Advanced (LTE-A), a technique called carrier aggregation is adopted. Carrier aggregation of LTE-A Release 11 (referred to below as R11) will be described briefly below.
In carrier aggregation of LTE-A Release 10 (referred to below as R10), only the cells with the same transmission timing are aggregated. However, in carrier aggregation of LTE-A Release 11, a group of cells with different transmission timings is aggregated and a TAG (timing advance group) is set for each group of cells by transmission timing.
For example, a primary timing advance group (pTAG) is set for a group of cells, with a first transmission timing, that includes primary cells (PCells). A secondly taming advance group (sTAG) is set for a group of cells, with a second transmission timing, that includes only secondly cells (SCells).
Accordingly, when detecting a deviation in the timing of a radio signal received from cells belonging to TAGs, the base station of R11 calculates the correction value of a TA for each TAG, includes the TA in the TAC, and notifies the mobile station of the TAC. At this time, the identifier of the TAG is included in the TAC to clearly indicate the TAG to which the cell to which the TA is applied belongs. The mobile station identifies the TAG (group of cells) based on the identifier included in the TAC and applies the TA to the group of cells belonging to the TAG.